Demand for flat panel displays has been increased as a society has become a sophisticated information society. Displays known as such flat panel displays encompass non light-emitting liquid crystal displays (LCD), light-emitting plasma displays (PDP), inorganic electroluminescence (inorganic EL) displays, and organic electroluminescence (organic EL) displays. Among them, the organic EL displays attract attention due to their light-emitting properties.
In a field of the organic EL displays, two display arts are well known. One of the two display arts is an art to display a moving image by driving organic EL elements in a simple matrix manner. The other of the two display arts is an art to display a moving image by driving organic EL elements in an active matrix manner by use of thin film transistors (TFTs).
A conventional display is such that each pixel unit includes a plurality of pixels for emitting red, green, and blue lights. Hence, each pixel unit can display various colors such as white so that a full color image can be displayed. In the case of the organic EL elements, red, green, and blue pixels are generally provided by providing different organic light-emitting layers by a mask deposition method using a shadow mask. This makes it possible to realize full color image display.
In this method, however, a mask processing accuracy, a mask alignment accuracy, and an increase in a mask size become serious issues. These issues become serious particularly in a filed of a large-size display such as a television device. In this filed, a substrate size becomes larger and larger. For example, the substrate size is 1500 mm×1850 mm in the sixth generation (G6). Then, it is increased to 2200 mm×2500 mm in the eighth generation (G8) and 2850 mm×3050 mm in the tenth generation (G10) sequentially. In a conventional method, a mask needs to have a size equal to or larger than a substrate size. In view of the circumstances, it is necessary to prepare or process a mask corresponding to a large substrate.
A mask is generally formed by a very thin metal. A film thickness of the mask is typically in a range of about 50 nm to 100 nm. This makes it very difficult to increase a mask size. Also, even in a case where a mask size is increased, there are deteriorations in mask processing and mask alignment accuracy. This may cause two or more light-emitting layers to be provided in a same region. Accordingly, lights emitted from the different light-emitting layers are adversely mixed in color and thereby cause deterioration in quality of display color. In order to prevent this problem, an insulating layer having a wide width is normally provided between pixels. However, in a case where an area of each pixel is fixed, this increases an area of a non light-emitting section. That is, there is a decrease in aperture ratio in each pixel. This causes a decrease in luminance, which in turn causes an increase in power consumption. This ultimately shortens a lifetime of the device.
According to a conventional manufacturing method of the organic EL display, an organic layer is deposited by placing a deposition material below a substrate and depositing an organic material upwardly in a vertical direction. However, there is a problem that as a substrate size is increased (as a mask size is increased), a mask deflects in the center. In a case where the mask deflects as such, there is caused the adverse mixture of lights of different colors. Further, the organic layer is formed only partially, and there is a risk that a current supplied to upper and lower electrodes leaks and thereby causes a failure. The aforementioned problem is similarly caused even in a case where the mask is thermally expanded.
In the conventional manufacturing method, a mask decays each time it is used. As such, one mask can be used only for the fixed number of times. Such limitation gives rise to a cost increase problem in a case where a mask size is increased. In fact, a cost issue has become a most serious problem in the field of the organic EL displays.
As described so far, as the substrate size is increased, the conventional method in which the different light-emitting layers are thus formed with the use of the shadow mask causes a very serious problem. As such, organic EL elements in a large-size substrate have not been successfully manufactured yet, and only organic EL elements in a substrate of half the size of G4 substrate size have been successfully manufactured.
In contrast, Patent Literature 1 proposes a method of outputting full color light by using a combination of (i) an organic EL element which has a light-emitting layer for emitting light in a range of a blue color to a turquoise blue color, (ii) a green pixel which has a fluorescent layer for emitting green light by absorbing the light in the range of the blue color to the turquoise blue color, emitted from the organic EL element, (iii) a red pixel which has a fluorescent layer for emitting red light by absorbing the light in the range of the blue color to the turquoise blue color, and (iv) a blue pixel which has a blue color filter to improve a color purity. According to the method, it is unnecessary to pattern an organic layer. For this reason, an organic EL element can be manufactured more easily at a lower cost, as compared to the case of the method in which the different light-emitting layers are formed with the use of the shadow mask. Further, because there is no limitation due to mask use, the organic EL element can be easily manufactured with a large-size substrate.
However, in a case where excitation light emitted from light source 104 enters a fluorescent layer 103 provided on a substrate 101, light emitted from the fluorescent layer 103 isotropically spreads (see FIG. 11). As such, a light component (see arrows 106 shown in full lines in FIG. 11) emitted to a light-extraction side (to a substrate 101) can be outputted to an outside as useful light, whereas light components (see arrows 107 shown in dashed lines in FIG. 11) emitted from a side surface of the fluorescent layer 103 and an opposite surface of the light-extraction side cannot be extracted to the outside. As such, there is a light emission loss. The light which can be actually extracted to the light-extraction side accounts for only about 10% of total light emission. This results in an increase in power consumption. As such, the light emission loss is considered as a serious problem in a field of display devices.
As a solution to the problem, Patent Literature 3 proposes a method of efficiently extracting, to a front side, light emitted from a side surface of a fluorescent layer. In the method, a reflecting film is provided on a side surface of the fluorescent layer so as to redirect the light to the front side. However, the method faces a problem that it cannot extract a light component emitted toward a light source side (a side opposite to a light-extraction side).
Each of Patent Literature 2 and Non-Patent Literature 1 proposes such a light-emitting display device obtained by applying a method of employing a fluorescent material to a conventional liquid crystal display device. Unlike the conventional liquid crystal display device, the proposed display devices are such that RGB fluorescent layers provided outside a liquid crystal layer emit light. As such, it is possible to realize the display devices which are excellent in viewing angle characteristics.
However, in each of the proposed light-emitting display devices, light emitted from the fluorescent layer isotropically spreads in the same manner as described above. This causes a similar problem that there is a huge loss of light extracted to the outside from the fluorescent layer, and, as a result, light-emitting efficiency of light thus obtained is reduced. Such a reduction in light-emitting efficiency results in an increase in power consumption. This becomes a serious problem in the field of display devices.